ORACLEASM-SCANDISKS(8) Oracle ASM Support Manual ORACLEASM-SCANDISKS(8)NAMEoracleasm-scandisks - Scan the system for ASM disks
SYNOPSIS
oracleasm scandisks [-l <manager>] [-v] [-s]
[[-o <order>] ...] [[-x <exclude>] ...]
[<device> ...]
oracleasm scandisks -h
oracleasm scandisks -V
DESCRIPTION
The scandisks command checks block devices for ASM disks. Disks tagged
for ASMLib will be added to the ASMLib kernel driver.
The scandisks command will scan all system devices by default,
reloading the partition table of each device. Devices can be excluded
from the scan and ordered in the scan. Specific devices can be scanned
exclusively. Finally, the partition tables can be left as-is to prevent
conflict with in-use disks.
OPTIONS
-l|--manager <manager>
Specifies the manager device used to connect to the ASMLib driver.
Almost always unnecessary, as only one manager device is in use.
-s|--scanonly
Do not reload the partition table. By default, the scandisks
command will reload the partition table of each device it
encounters. This can cause a transient I/O error for devices that
are in use. The -s option will prevent the partition table reload,
allowing for a completely safe scan of in-use devices.
-o|--scanorder <pattern>
Scan disks matching PATTERN first. The -o option can be specified
multiple times, in order of precedence (first is highest). See the
section [SCAN PATTERNS] below. This option has no effect if devices
are specified on the command line.
-x|--scanexclude <pattern>
Exclude disks matching PATTERN from any scan. The -x option can be
specified multiple times. See the section [SCAN PATTERNS] below.
This option has no effect if devices are specified on the command
line.
-v|--verbose
Verbose operation. This will print any debugging information.
<device>
A path to a device to scan. If devices are specified on the command
line, only those devices are scanned, and the -x and -o options are
ignored. If no devices are specified, scandisks will attempt to
scan all block devices in the system.
-h|--help
Display usage information.
-V|--version
Display version information.
SCAN PATTERNS
The -o and -x options take a PATTERN to match device names. It is a
simple substring match. It matches against the device path without the
leading /dev/. For example, the PATTERN "sd" will match "/dev/sda" and
"/dev/sdb", but not "/dev/hda". The pattern "cciss/" will match all
CCISS devices "/dev/cciss/*", where "cciss/c0" will match all devices
on CCISS controller 0.
Note that PATTERN is matched against names in /proc/partitions.
HOW SCANNING HAPPENS
The scan proceeds in four basic stages.
First, the list of disks to scan is created. If disks were specified on
the command line, this is the list. If not, /proc/partitions is read,
and each block device is added, subject to the -o and -x options.
Second, the partition tables of each disk in the scan are reloaded
unless the -s option was specified. Any disks that no longer exist are
dropped.
Third, the list of disks is recreated based on the new partition
tables.
Finally, each disk in the list is checked to see if it is marked for
ASM use. Disks that are marked are instantiated.
MANAGING DISKS IN A CLUSTER
The Oracle ASM Library, by design, does not talk to other nodes in a
cluster. This is the job of the ASM software. The ASM Library merely
provides an interface from ASM to the disks. However, the ASM Library
does ensure that the same LABEL is used to see a disk on all nodes.
Thus, while each node may have a different device file (/dev/sda1 vs
/dev/sdc1), The ASM Library will see the label VOL1, and all nodes will
know they are accessing the same physical disk.
In a cluster, creation and removal of ASM disks is a two step process.
1. Create (oracleasm-createdisk(8)) or remove (oracleasm-
deletedisk(8)) the disk on any one node in the cluster.
2. Scan (oracleasm-scandisks(8)) the volumes on all other nodes in
the cluster.
Step (1) may be repeated as many times as necessary, adding and/or
removing multiple disks. Once all disk changes have been made, a single
call to scandisks is made on the other nodes. It will pick up all
changes at once. When configuring 100 disks, while 100 createdisk
commands need to be run on one node (possibly via a script), only one
scandisks command needs to be run on every other node.
As scandisks is run when the ASM Library driver starts up, changes are
also seen by nodes that are newly created.
SAFELY MANAGING DISKS
The Oracle ASM Library and its driver are an interface to disks. They
are not cluster-aware, and do not communicate with the ASM process or
other nodes. Thus, care must be taken when adding and removing disks.
When a disk device supports partitioning (eg, with fdisk(8) or
parted(8)), oracleasm-createdisk(8) will refuse to consider the entire
unpartitioned disk. The disk must be partitioned and that partition be
marked for ASM use. Access to unpartitioned disks has been specifically
disallowed as we have seen higher incidence of accidental repartitions
(thus overwriting ASM data) with unpartitioned than partitioned disks.
Disks that cannot be partitioned (eg, loop and md devices) are not
subject to this restriction.
When marking a disk with oracleasm-createdisk(8), make sure that the
disk partition in question is not being used elsewhere on the SAN.
When removing a disk with the oracleasm-deletedisk(8) command, make
sure that the ASM disk is not used by any ASM process anywhere on the
SAN.
Care must also be taken when running the oracleasm-scandisks(8)
command. Use the -s option when disks that are being scanned are
already in use by ASM processes. If in-use disks do not need to be
scanned, they can be excluded with the -x option. Finally, the disks
needing to be scanned can be explicitly specified on the scandisks
command line.
EXAMPLES
oracleasm scandisks
Scan all block devices for ASM disks.
oracleasm scandisks -s
Scan all block devices, but do not reload their partition tables.
oracleasm scandisks /dev/sda* /dev/sdb*
Scan only /dev/sda* and /dev/sdb*.
SEE ALSOoracleasm-init(8), oracleasm-dropdisks(8), oracleasm-exit(8)AUTHOR
Oracle Corporation
COPYRIGHT
Copyright 2007, 2008 Oracle. All rights reserved.
ORACLEASM
Part of the oracleasm(8) support tools.
oracleasm-support 2.1.4 04/21/2009 ORACLEASM-SCANDISKS(8)
